In manufacturing a semiconductor device, a substrate processing system including a plurality of processing chambers is used to perform various processes on a substrate to be processed such as a semiconductor wafer or the like. Generally, the substrate processing system includes: a mounting unit for mounting thereon a FOUP (Front Opening Unified Pod) as a transfer container accommodating therein several tens of substrates; a processing unit for performing predetermined processing on a substrate; and a substrate transfer chamber provided between the mounting unit and the processing unit.
A fan filter unit (FFU) for supplying clean air or a clean gas, e.g., N2 gas or the like, into the substrate transfer chamber, is provided at a ceiling portion of the transfer chamber. In the substrate transfer chamber, a highly clean environment without particles can be maintained by forming downward flow by the clean gas and by increasing an internal pressure to protect the substrate from particle contamination (e.g., Japanese Patent Application Publication No. H11-63604 (Patent Document 1) and Japanese Patent Application Publication No. 2004-311940 (Patent Document 2)).
An operator may enter the substrate transfer chamber during a maintenance operation or the like. Therefore, a gas in the substrate transfer chamber needs to be replaced before and after the maintenance operation. For example, it is required to replace N2 gas in the substrate transfer chamber with clean air before the maintenance operation and replace the clean air in the substrate transfer chamber with N2 gas after the maintenance operation. It is preferable to set the gas replacement time to be considerably short in order to reduce a period of time in which the entire substrate processing system is stopped. When the clean air is replaced with N2 gas, a large amount of N2 gas is required until the substrate transfer chamber is filled with N2 gas and, thus, reduction of the amount of N2 gas is also required.
There is suggested a technique for improving a throughput of a pressure switching operation by providing a volume varying mechanism for varying a volume in a load-lock chamber which is switched between a vacuum state and an atmospheric pressure state in a substrate processing system (e.g., Japanese Patent Application Publication No. 2005-333076 (Patent Document 3)). The volume varying mechanism has a single-purpose actuator to move a movable plate.